The present invention relates to a rectangular optical glass lens and a manufacturing method thereof, especially to a rectangular optical glass lens with optical surface, right-angular circumference, and low cost that is applied to camera phones, other cameras with image sensors such as Charge-Charged Device (CCD), or Complementary Metal-Oxide Semiconductor (CMOS).
A lot of electronics such as digital cameras, PC cameras, network cameras, mobile phones or personal digital assistance (PDA) are required to be equipped with image capturing devices. For easy carrying and requirements of users, the image capturing device not only has good image quality, but also has compact size as well as low cost so that it has more applications. The glass precision molding technology has been applied to produce aspherical molded glass lens with high resolution, good reproduction and low cost such as lens teached in patents, US2006/0107695, US2007/10043463, TWO95101830, TW095133807, JP63-295448 etc. A glass preform is set into a forming mold to be heated and softening. Then increase pressure on an upper mold and a lower mold of the forming mold so as to transfer the soft glass perform become the same shapes as the surfaces of upper mold and lower mold. After cooling, a molded glass lens is released. In order to reduce the manufacturing cost, U.S. Pat. No. 7,312,933 disclosed a rectangular monobloc optical lens 1a is made from a cut rectangular glass unit being molded, as shown in FIG. 1. Refer to JP63-304201 and US Pub. No. 2005/041215, lens arrays manufactured by press-molding are disclosed. Refer to JP02-044033, a plate glass 2a of FIG. 2, heated-press and repeatedly shift the molds to perform forming of lenses. Then the individual lens 1b in FIG. 2 is obtained by cutting the plate glass 2a. Refer to US 2004/165095, a lens with an infrared ray filter produced by a multi-cavity glass molding method is disclosed. A dielectric multilayer film is provided on one of the surface of a glass plane-convex lens and then being cut into a plurality of infrared ray filters.
Although the multi-cavity molding method can be applied to glass molding technique, such way is only feasible in producing spherical lens, plano-convex, and plano-concave lenses. While applying to aspherical lens in mini-cameras or camera phones, there is residual air in the mold cavity while the process of heating and pressing. This reduces precision of the aspherical glass lens. There are several ways to solve the problems of residual air. For example, refer to JP2002-003225, JP05-286730, JP06-191861, US 20050172671, and EP0648712 etc, the problem of residual air is solved by pressure control, temperature control or surface roughness. Refer to JP61-291424, TWI248919, JP2000-044260, TW200640807, US2005/0242454, air channels are disposed on the mold so as to release residual air. Yet a lot of melt glass will overflow into the air-exhaust channel to form the brim. A further processing is required to shape the brim. Or as shown in JP61-291424, JP08-337428, and U.S. Pat. No. 7,159,420, a groove or a ventilative hole is disposed on the molding unit, especially the lower molding unit. But by such design, corresponding protrudent may occur on the molded lens and this lead to problems in following processing or assembling.
Generally, air exhaust effect is represented by air-exhaust efficiency δ that equals to the cross-sectional area of air-exhaust channels divided by volume of the mold cavity (δ=cross-sectional area of air-exhaust channels/volume of the mold cavity). The larger the air-exhaust efficiency δ is, the less air accumulates during the molding process. On the contrary, if the air-exhaust efficiency δ is getting smaller, it's difficult to release the air. In order to release air effectively, δ larger than 0.25 is preferred. As to the Multi-Cavity mold, especially the cavity near the center of the mold core, it's getting difficult to release the air. After long-term experiments, the results show that as to rectangular glass, δ value of the mold cavity near edges of the mold should be larger than 0.25. The δ value of the mold cavity should be proportional to the distance from the mold cavity to the mold, increasing in a geometric series. Therefore, while producing multi-cavity optical glass lens by precision molding glass technique, the mold should be designed with higher δ value without forming protrudent on the lens so as to meet requirements of easy mass-production and high yield rate.